EPS is originated from the addition of blowing agents to polystyrene (PS) in order to obtain the PS as a foamed structure: a matrix comprised of fixed or flexible, coherent structural elements of PS that constitute spatial open or closed cells or cavities in which air and/or blowing agents are contained, whether free or entrapped.
EPS has found widespread use in insulation of heat; absorbtion of noise, vibration and shocks; light-weight-structured material in sandwich panels and transport packages; foamed packaging chips; etc.
The voluminous nature of EPS, especially in the state of waste, creates a problem in that high logistic costs per ton polymer are involved in handling and transport. A truckload of EPS, having a mean density of 25 kg/m.sup.3, only contains 800 to 1000 kg PS.
A reduction of volume, for instance, can be obtained by mechanical means like pressing or treatment between compactor rolls. This type of equipment, especially the roll compactor, is precious and takes relative large amounts of energy to do the job. Especially for the elastic types of foam, mechanical systems perform less efficiently. Furthermore it is difficult to keep polluting blowing agents like CFK's, present in the older types of EPS, from entering the environment during the compacting process.
Methods, among others, are known from the literature in which polymers are brought into contact with solvents for those polymers. These methods lead to more or less homogeneous solutions of either low or high viscosity, mainly applied as adhesives. DE-C1 37 41 777 is related to waste PS that, in contact with solvents, leads to PS solutions with adhesive properties. DE-A1 31 13 125 is related to EPS that, in contact with "stain remover", leads to a solution with adhesive properties. DE-A1 23 03 754 is related to EPS that, in contact with chlorinated hydrocarbons, in particular highly chlorinated hydrocarbons and at higher temperatures, leads to sticky masses with adhesive properties.
A need remains to convert waste EPS in an effective way in a form that, on the one hand, leads to economic advantage by lowering logistic costs related to collecting, handling, storage and transport and, on the other hand, offers the opportunity for reprocessing, whether physically to PS, or chemically to monomer styrene and other raw materials, in that a certain amount of contamination and incompatibility due to the presence of sticker labels, printing ink, other polymers, adhering sand, organic matter, etc. is not objectionable.